Graphiccard does not run correctly

First i have to say, that my english isn't the best, but i will try my best.

I have cleaned my pc hardware and after i run a benchmarktest, the fan of my graphiccard runs 100% and my screen went black. Before i cleaned my hardware the benchamarktest runs till the end.

When I use the pc without playing games, sometimes the graphiccard runs 90% for the first time I switch e.g. a tab in my browser but falls back to normal speed after some seconds.

2 screws broke in the thread after I want fix the cooler onto the graphiccard. Could it be that the cooler does not sit correctly onto the graphiccard? Additionally the fan is louder than before. The graphiccard sits perfectly in the slot and all cables are there where they should be.